All things being equal, yes steel toed boots will result in more calories burned, because steel toed boots weigh more than the average casual shoe or street shoes. For example, this pair is 4.3 lbs.
This article (The Telegraph) suggests that heavy shoes "work a lot like ankle weights", and this study concluded that "oxygen uptake and heart rate responses were greater" with ankle weights than with no weights.
However, I could not find any study on PubMed or Google Scholar that examined prescribing steel toed boots as an intervention to see if all other things actually do remain equal (you maintain the same activity level, they don't cause injuries, among other things), and whether more calories are actually burned in practice.
In summary, the mechanism is sound, but its practical effectiveness hasn't been demonstrated (as far as I can tell).